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Chapter 6 Detailed Answers to Assess Your Understanding 1. b: To analyze the atrial activity of an ECG you assess the P waves. 2. b: The amplitude of the P wave normally does not exceed 2.5 mm high. Its duration is normally 0.06 to 0.10 seconds. 3. d: An upright, round P wave (in lead II) that precedes each QRS complex indicates that the electrical impulse originated in the SA node and was carried through the atria in a normal manner. 4. d: The characteristic considered normal (in lead II) is a rounded and upright P wave. 5. c: With ECG waveforms, the lead you select affects your ability to assess their morphology. As such, the answer for this question is the P waves are best evaluated by choosing the appropriate lead. 6. b: With increased left atrial pressure and left atrial enlargement, the P wave is normally notched or wide. 7. a: Enlarged or damaged atria produce P waves that look different than sinus P waves. Tall and symmetrically peaked P waves suggest increased right atrial pressure and right atrial enlargement. Notched or wide (prolonged) P waves indicate increased left atrial pressure and left atrial enlargement. 8. a: An impulse that arises closer to the SA node has the same appearance as a normal P waves. In contrast, if the impulse arises from the lower-right atrium, near the AV node or in the left atrium, depolarization occurs in a retrograde direction resulting in the P’ wave being inverted in lead II. 9. c: Early beats that arise from the atria may have P’ waves which are buried in the T wave of the preceding beat. This can cause the T wave to appear notched or different than other T waves in the tracing. 10. b: With tachycardia that arises from the atria, the P’ wave looks different than P waves that arise from the SA node. 11. a: An atrial pacemaker site that changes from location to location has P waves that continually change in appearance. 12. a: When the atria fire faster than 350 beats per minute, the P waves are indiscernible; instead, there is a chaotic-looking baseline. 13. b: Dysrhythmias that arise from AV junctional tissue have inverted P’ waves. 14. d: With ventricular dysrhythmias, the P’ waves are absent. 15. c: AV heart block has more P waves than QRS complexes. 16. d: the patient’s dysrhythmia originated from the atria. 17. d: The firing rate of the F waves is 144 beats per minute.